Chapter 24 Transition Metals Flashcards
What are transition elements?
Elements with at least one ion with an incomplete d sub shell
State the elements in period 4 which are not considered as transition elements.
Scandium- only forms Sc^3+ ion
No electrons in d subshell
Zinc- only forms Zn^2+ ion
Contains a full d subshell
How does the electron configuration of Chromium and Copper differ from other transition elements?
One of the electrons from the 4s subshell is promoted to the 3d subshell in order to achieve a stable arrangement of lower energy which reduces repulsion.
When d block elements form ions what subshell are the electrons lost from?
Because the 4s sub shell is at a lower energy (electrons always fill from the lower energy levels first) than the 3d sub shell, this means that the 4s sub shell fills before the 3d sub shell consequently this means that the 4s sub shell also empties before the 3d sub shell.
What are the general properties of transition elements?
Can show more than one oxidation state in compounds (variable oxidation state)
Can form coloured ions
Can act as catalysts
What are the different oxidation states of Mn in KMnO4 compared to MnO2?
Mn oxidation state in KMnO4 is +7
Mn oxidation state in MnO2 is +4
What are the different oxidation states of Cr in Cr2O7^2- and [Cr(H2O)6]^3+?
Cr oxidation state in Cr2O7^2- is +6
Cr oxidation state in [Cr(H2O)6]^3+ is +3
Why are transition elements able to show variable oxidation states?
Because the energy levels of the 4s and 3d sub shells are very close to one another so different numbers of electrons can be lost or gained using similar amounts of energy.
What is a heterogenous catalyst?
The catalyst and reactants are in different physical states
State examples where transition metals act as heterogenous catalysts?
-Fe in the Haber process
-Ni in the hydrogenation of alkenes to alkanes
-MnO2 decomposition of hydrogen peroxide
How do transition elements act as heterogeneous catalysts?
The reactants ADSORB to the surface of the transition metal catalyst and weakens the bonds in the reactants
The reaction then takes place and products form The products leave the surface of the catalyst by desorption.
What are homogenous catalysts?
Where the catalyst and reactants are in the same physical state.
State an example where a transition element acts as a homogeneous catalyst and describe how it works.
The reaction between Iodide and Peroxodisulfate ions requires the Fe^2+ / Fe^3+ ions to catalyse the reaction as they both have same charge, so reaction alone would occur too slowly.
This works as Fe uses its ability to be able to change oxidation states in order to catalyse the reaction.
What is a catalyst?
A substance which increases the rate of a chemical reaction by providing an alternative pathway for the reaction to occur with a lower activation energy.
What are the advantages of using catalysts?
Allow process to operate at lower temperatures so lower energy consumption and carbon emissions.
Allow alternative reactions to occur with higher atom economies so less waste is produced
Allow alternative reactions with less toxic reactants
What is a complex ion?
A central metal ion surrounded by ligands
What is a ligand?
A molecule that donates a pair of electrons to central metal ion to form a co ordinate bond
What is a co ordinate bond?
A shared pair of electrons between two atoms where both electrons come from the same atom
What is the co ordination number?
The total number of co ordinate bonds formed between ligands and the central metal ion
State the different types of ligands?
Monodentate
Bidentate
Multidentate
What is a monodentate ligand?
A ligand that can form one co ordinate bond with the central transition metal ion
State examples of monodentate ligands
Water
Ammonia
Chloride ion
What is a bidentate ligand?
A ligand that can form two co ordinate bonds with the central transition metal ion.
State example of bidentate ligands
Ethanedioate C2O4^2-
O O
|| ||
C——C
/ \
: O - - O:
Ethane-1,2-diamine (en)
. . . .
NH2CH2CH2NH2
